Tripod type constant velocity joint

ABSTRACT

A tripod type constant velocity joint comprising a hollow cylindrical housing fixed to the end of a first rotary shaft and formed at the inner peripheral surface thereof with axially extending recessed grooves opened at one axial end and located at circumferentially trisectional positions on the inner peripheral surface, a tripod consisting of a boss fixed to the end of a second rotary shaft, and end-spherical trunnion journals radially projecting from circumferentially trisectional positions on the boss, a roller assemblies each consisting of an inner roller swingably fitted at the inner peripheral surface thereof on the spherical outer peripheral surface of the trunnion journal, and an outer roller supported for rotation and axial movement on the outer peripheral surface of the inner roller through needle rollers, wherein the outer rollers are received in the recessed grooves in the housing and are rollable axially of the housing, each recessed groove consists of guide surfaces contacting the outer peripheral surface of the outer roller and subjected to loads, and guide shoulder surfaces for guiding the outer roller axially of the housing, and only the side of the outer diameter of said boss associated with the end of the second rotary shaft is heavily chamfered. A relief is locally formed along the forged parting line of the trunnion journal. The root of the tripod journal is of non-circular cross-section in which the diameter as measured circumferentially of the joint is larger than the diameter as measured axially of the joint.

CROSS REFERENCE TO RELATED APPLICATION

This is a Divisional Application, which claims the benefit of pendingU.S. patent application Ser. No. 11/514,918, filed Sep. 5, 2006, whichis a Divisional of U.S. patent application Ser. No. 10/689,520, filedOct. 21, 2003. The disclosures of the prior applications are herebyincorporated herein in their entirety by reference.

BACKGROUND ART

The present invention relates to a tripod type constant velocity jointused for transmission of a rotary force between rotary shaftsincorporated in the driving system, for example, of an automobile andnon-linearly existing therein.

Tripod type constant velocity joints are in wide use as a kind ofconstant velocity joint to be incorporated in the driving systems ofautomobiles. For example, Japanese Patent Laid-Open Publication Sho62-233522 discloses a tripod type constant velocity joint 1 as shown inFIGS. 15 and 16. This tripod type constant velocity joint 1 comprises ahollow cylindrical housing 3 fixed to the end of a first rotary shaft 2,such as a driving shaft, and a tripod 5 fixed to the end of a secondrotary shaft 4, such as the rotary shaft on the wheel side.

The inner peripheral surface of the housing 3 is formed, atcircumferentially trisectional positions, with recessed grooves 6extending axially of the housing 3. On the other hand, the tripod 5comprises a boss 7 to be fixed to the end of the second rotary shaft 4,and columnar trunnion journals 8 radially projecting from thecircumferential trisectional positions on the boss 7. Each trunnionjournal 8 supports a roller 9 for rotation and more or less axialdisplacement through needle rollers 10. And these rollers 9 are fittedin the recessed grooves 6 in the housing 3, thereby constituting thetripod type constant velocity joint 1. In addition, a pair of guidesurfaces 6 a defining each recessed groove 6 are each an arcuatelyrecessed surface, and each roller 9 is supported for rolling andswinging between these guide surfaces 6 a.

During the use of the tripod type constant velocity joint 1 constructedas described above, when, for example, the first rotary shaft 2 isrotated, its rotary force is transmitted from the housing 3 to the boss7 of the tripod 5 successively through the rollers 9, needle rollers 10,and trunnion journals 8, rotating the second rotary shaft 4. Further,when the center axis of the first rotary shaft 2 is out of alignmentwith the center axis of the second rotary shaft 4, that is, when thetripod type constant velocity joint 1 takes an operating angle, with therotation of the two rotary shafts 2 and 4, each trunnion journal 8 isdisplaced in a direction to swing around the axis of the tripod 5 withrespect to the guide surfaces 6 a of the corresponding recessed groove6, as shown in FIGS. 15 and 16. At this time, the roller 9 supported byeach trunnion journal 8 rolls on the guide surfaces 6 a of the recessedgroove 6 while being displaced axially of the trunnion journal 8. Thesemovements secure equality of velocity between the first and secondrotary shafts 2 and 4.

In the case of the tripod type constant velocity joint 1 constructed toact in the manner described above, when the first and second rotaryshafts 2 and 4 are rotated with an operating angle taken, each roller 9performs a complicated motion. That is, each roller 9 moves along theguide surfaces 6 a while changing its direction axially of the housing 3and is displaced axially of the trunnion journal 8. When each rollerperforms such complicated motion, relative displacement between theouter periphery surface of each roller 9 and the guide surfaces 6 a isnot necessarily smoothly effected, so that relatively large friction isgenerated between these surfaces. As a result, in the case of the tripodtype constant velocity joint of the construction shown in FIGS. 15 and16, a tertiary axial force is generated per revolution. And it is knownthat a vibration called shudder is generated in remarkable cases as whenit is incorporated into an automobile to transmit a large torque with alarge operating angle taken.

As measures against the above problem, French Patent No. 2752890discloses a construction as shown in FIG. 17 a and Japanese PatentLaid-Open Publication Heisei 3-172619 discloses a construction as shownin FIG. 19. The construction of FIG. 17 a is such that a roller assembly(inner and outer rollers relatively rotatable through needle rollers) isparallelly guided in a recessed groove in the housing and such thatcentering and swinging are made possible between the spherical innerperipheral surface of the inner roller and the spherical trunnionjournal, and spherical fitting is ensured in that the generating line ofthe outer peripheral surface of the spherical trunnion journal is an archaving a radius of curvature, r_(T), smaller than the radius (A/2) ofthe trunnion journal. In this case, the major diameter of a contactellipse generated under a load torque between the inner roller sphericalinner peripheral surface and the spherical trunnion journal becomeslonger. Increasing a spherical surface clearance {(C−A)/2} makesspherical fitting possible without having to make the radius ofcurvature, r_(T), smaller than A/2. In that case, however, not only doesthe rotation-directional play become larger but also the contact areabecomes smaller, resulting in a disadvantage leading to rotationdurability decreasing with increasing contact surface pressure.

With the construction of FIG. 19, since a torque load is imposed betweenthe cylindrical inner peripheral surface 20 of the inner roller and thespherical trunnion journal 8, the contact surface area furtherdecreases, resulting in a disadvantage leading to rotation durabilitydecreasing with increasing contact surface pressure. Further, the width(corresponding to the contact ellipse minor diameter) of the contactsurface further decreases and the circumferential contact lengthcorresponding to the major diameter further increases. The contactsurface pressure is also high.

In these prior art tripod type constant velocity joints, a swing slipthat takes place on the contact ellipse due to the swing of the trunnionjournal when the joint is rotating under a load with an operating angletaken acts, as shown in FIG. 18, as a spin moment tending to change therolling direction of the roller assembly, so that the roller assemblyhas its direction changed until it contacts the guide surfaces of therecessed groove in the housing, and the contact force becomes greater.Further, since it is no longer parallel with the recessed groove in thehousing, it is thought that smooth rolling is impeded and the rollingresistance cannot be fully reduced.

A main object of the invention is to provide a tripod type constantvelocity joint that has solved the above problems. That is, theinvention is intended to provide a tripod type constant velocity jointwherein while holding small the clearance between the sphericallysurface-fitting inner roller and spherical trunnion journal, that is,holding the rotation-directional play small, spherical fitting (surfacepressure reduced) is made possible and the contact ellipse majordiameter is reduced so as to keep small the spin moment generated by theswing of the trunnion journal, so as to minimize the rolling resistancein the roller assembly during the rolling with an operating angle taken,thereby ensuring the coexistence of reduced shudder and high durabilitywhen the joint is assembled to an automobile.

DISCLOSURE OF THE INVENTION

According to an embodiment of the invention, a tripod type constantvelocity joint comprises a hollow cylindrical housing fixed to the endof a first rotary shaft and formed with axially extending recessedgrooves opened at one axial end and located at circumferentiallytrisectional positions on the inner peripheral surface, a tripodconsisting of a boss fixed to the end of a second rotary shaft, andend-spherical trunnion journals radially projecting fromcircumferentially trisectional positions on the boss, roller assemblieseach consisting of an inner roller swingably fitted at the innerperipheral surface thereof on the spherical outer peripheral surface ofthe trunnion journal, and an outer roller supported for rotation andaxial movement on the outer peripheral surface of the inner rollerthrough needle rollers, wherein the outer rollers are received in therecessed grooves in the housing and are rollable axially of the housing,each recessed groove consists of guide surfaces contacting the outerperipheral surface of the outer roller and subjected to loads, and guideshoulder surfaces for guiding the outer roller axially of the housing,and only the side of the outer diameter of said boss associated with theend of the second rotary shaft is heavily chamfered. This embodiment isarranged so that during assemblage by tilting the roller until theprojected shorter radius of the trunnion journal (in a direction atright angles with the load-subjected side) is reduced to not more thanits inner diameter at its end on the inner roller fitting side, theroller does not interfere with the boss of the tripod (journalunderhead). Since torque transmission between the tripod and the secondrotary shaft is effected mostly by the second rotary shaft non-end sidein the boss, heavily chamfering the boss at the second rotary shaft enddoes not lead to a lowering in the boss strength. Mounting this tripodtype constant velocity joint on a vehicle makes it possible to reducethe vibration of the vehicle and to ensure coexistence of high strengthand durability.

The load-subjected position (contact ellipse center position) on thespherical outer peripheral surface of the trunnion journal may beprovided with a flat surface or dent of suitable size. The flat surfaceor dent is located in the region inwardly receding from the sphericalouter peripheral surface of the trunnion journal and has an optionalsize within a range where the contact area decreases, for example, to ⅕of the contact area due to spherical fitting without such flat surfaceor dent. There is almost no relative displacement in the center of theregion of spherical contact between the trunnion journal and the innerroller, in which poor lubrication could occur, and smearing measures canbe taken by providing said flat surface or dent so as to avoid contactin said region.

At least one end of the inner peripheral surface of the outer roller maybe integrally formed with a needle roller retainer. Thus, by forming theouter roller integrally with an inner needle roller retainer and anouter needle roller retainer, it is possible to constitute a rollerassembly by only three elements, the inner roller, needle rollers andouter roller, reducing the number of parts. In this case, the relationDi<do can be established where Di is the inner diameter of thecylindrical inner peripheral surface of the outer roller at the jointinner diameter side end and do is the outer diameter of the innerroller. Adopting such arrangement makes it difficult for the outerroller to be detached from the inner roller in the state of the tripodkit (a unit consisting of the tripod and the roller assembly), makinghandling easy.

At least one end of the outer peripheral surface of the inner roller maybe integrally formed with a needle roller retainer. By forming the innerroller integrally with an inner needle roller retainer and an outerneedle roller retainer, it is possible to constitute a roller assemblyby only three elements, the inner roller, needle rollers and outerroller, reducing the number of parts. In this case, the relation Di<docan be established where do is the outer diameter of the cylindricalouter peripheral surface of the inner roller at the joint inner diameterside end and Di is the inner diameter of the outer roller. Adopting sucharrangement makes it difficult for the outer roller to be detached fromthe inner roller in the state of the tripod kit, making handling easy.

According to another embodiment, a tripod type constant velocity jointcomprises a hollow cylindrical housing fixed to the end of a firstrotary shaft and formed with axially extending recessed grooves openedat one axial end and located at circumferentially trisectional positionson the inner peripheral surface, a tripod consisting of a boss fixed tothe end of a second rotary shaft, and end-spherical trunnion journalsradially projecting from circumferentially trisectional positions on theboss, roller assemblies each consisting of an inner roller swingablyfitted at the inner peripheral surface thereof on the spherical outerperipheral surface of the trunnion journal, and an outer rollersupported for rotation and axial movement on the outer peripheralsurface of the inner roller through needle rollers, wherein the outerrollers are received in the recessed grooves in the housing and arerollable axially of the housing, each recessed groove consists of guidesurfaces contacting the outer peripheral surface of the outer roller andsubjected to loads and guide shoulder surfaces for guiding the outerroller axially of the housing, and a relief is locally formed along theforged parting line of the trunnion journal, thereby receding theprotuberance of the forged parting line inwardly from the outerperipheral surface of the trunnion journal. Providing a relief resultsin the protuberance of the forged parting line not projecting beyond theouter peripheral surface of the trunnion journal, thus making itpossible to effect spherical fitting surface contact between the innerroller and the trunnion journal without the operation of removing theprotuberance of the forged parting line, and the surface pressurelowers. Therefore, it is possible to provide a tripod type constantvelocity joint ensuring the coexistence of reduced shudder with thejoint assembled to a vehicle, high durability and cost reduction.

The cross-section of the trunnion journal in the torque load region maybe substantially double spherical. In that case, the parting lineposition on the trunnion journal recedes from the inner sphericalsurface of the inner roller toward the minor diameter side, so that arelief is formed without taking special measures. In a torque-loadedstate, the contact regions between the trunnion journal and the innerroller are located in two positions symmetrical with respect to theforged parting line of the trunnion journal, but their abutment occursin their spherical surfaces, so that there is no danger of edge loading.As a concrete embodiment of said substantially double spherical shape,an example may be mentioned in which the radius R of the doublespherical surface of the trunnion journal is set so that r/2<R<r where ris the radius of curvature of the spherical inner peripheral surface ofthe inner roller.

Let θ be the angle at which the roller assembly is tilted when assembledto the trunnion journal. Then, by setting the maximum diameter φ D ofthe trunnion journal (including the forged parting line) projected inthe direction of angle θ not more than the inner diameter φ d of theinner roller on the insertion side, it is possible to assemble theroller assembly to the trunnion journal without elastically deformingthe inner roller during incorporation. Therefore, according to thisembodiment, it becomes possible to omit the forged parting line removingstep and the force fitting step required for assembling the rollerassembly to the trunnion journal. Further, a notch may be locally formedin the inner diameter of the inner roller on the insertion side, and thesetting may be such that φ D₂<φ d₂ where φ d₂ is the inner diameter ofthe notch and φ D₂ is the maximum diameter of the trunnion journal(including the forged parting line) projected in the direction of angleθ.

The setting may be such that with θ₁ being the angle at which the rollerassembly is about to separate from the trunnion journal, the rollerassembly interferes with the rotary shaft when it is tilted up to anangle θ₂ (θ₂<θ₁) after the rotary shaft has been mounted in a tripodkit. Herein, a unit consisting of a tripod and roller assemblies istermed a tripod kit. Further, the term “rotary shaft” shall include notonly the rotary shaft itself but also a separate member, such as a stopring, attached to the rotary shaft. Employing such arrangement ensuresthat in the state of the unit consisting of the tripod and rollerassemblies, that is, tripod kit, the tripod is assembled to the secondrotary shaft, and once a stop ring is mounted, the inner rollerinterferes with the stop ring or the rotary shaft and cannot tilt up tothe angle θ₁ at which it separates from the trunnion journal, so thatthe tripod kit and the rotary shaft assume a unit handling state, whichgreatly facilitates handling.

According to another embodiment of the invention, a tripod type constantvelocity joint comprises a hollow cylindrical housing fixed to the endof a first rotary shaft and formed at the inner peripheral surfacethereof with axially extending recessed grooves opened at one axial endand located at circumferentially trisectional positions on the innerperipheral surface, a tripod consisting of a boss fixed to the end of asecond rotary shaft, and end-spherical trunnion journals radiallyprojecting from circumferentially trisectional positions on the boss,roller assemblies each consisting of an inner roller swingably fitted atthe inner peripheral surface thereof on the spherical outer peripheralsurface of the trunnion journal, and an outer roller supported forrotation and axial movement on the outer periphery of the inner rollerthrough needle rollers, wherein the outer rollers are received in therecessed grooves in the housing and are rollable axially of the housing,each recessed groove consists of guide surfaces contacting the outerperipheral surface of the outer roller and subjected to loads, and guideshoulder surfaces for guiding the outer roller axially of the housing,it being arranged that when the roller assembly is to be assembled tothe trunnion journal, it is done so by tilting the roller assemblyaxially of the joint, the root of the tripod journal being ofnon-circular cross-section in which the diameter measuredcircumferentially of the joint is larger than the diameter measuredaxially of the joint. As for a non-circular shape in which the diametermeasured circumferentially of the joint is larger than the diametermeasured axially of the joint, there may be mentioned, for example, anelliptic shape with its minor axis directed axially of the joint.Assembling the roller assembly to the trunnion journal by tilting it ina plane including the direction of the axis of the joint makes itessential only that the interference-avoiding relief for assembling thejournal underhead and the roller to each other be present only on theside of the journal underhead as seen axially of the joint, so that theinterference-avoiding relief for assemblage on the side thereof as seencircumferentially of the joint becomes unnecessary. In the case of suchdesign specification, since there is no interference-avoiding relief inthe underhead circumferential position tending to be the maximum stressposition when subjected to torque load, strength improvement becomespossible and it is possible to provide a more compact joint.

These and other objects and arrangements of the invention will becomemore apparent from the following description to be given with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a cross-sectional view of a tripod type constant velocityjoint showing an embodiment of the invention, and FIG. 1 b is a partialenlarged view of FIG. 1 a;

FIG. 2 is a longitudinal sectional view of the tripod type constantvelocity joint of FIG. 1 a;

FIG. 3 is an exploded sectional view of a tripod kit, illustrating howto assemble a roller assembly to a trunnion journal;

FIGS. 4 a-4 c are side views of the trunnion journal FIGS. 5 a and 5 b,and FIGS. 6 a and 6 b are sectional view of the trunnion journal and theroller assembly;

FIG. 7 a is a side view of the trunnion journal, FIG. 7 b is across-sectional view of the trunnion journal, and FIG. 7 c is anenlarged view of a forged parting line projection of FIG. 7 b;

FIG. 8 a is a side view of the trunnion journal, and FIG. 8 b is across-sectional enlarged view of a contact region between the trunnionjournal and an inner roller;

FIG. 9 a is a front view of the trunnion journal, FIG. 9 b is a sideview of the trunnion journal, and FIG. 9 c is an enlarged view of thearea C of FIG. 9 a;

FIG. 10 is a cross-sectional diagram of the contact region between thetrunnion journal and the inner roller;

FIG. 11 is a sectional view of the tripod kit;

FIG. 12 a is a front view of the tripod, and FIG. 12 b is a sectionalview taken along the line b-b in FIG. 12 a;

FIG. 13 is an exploded sectional view of a tripod kit similar to thatshown in FIG. 3;

FIG. 14 a is a sectional view of the inner roller, and FIG. 14 b is aview taken in the direction of arrow Y in FIG. 14 a;

FIG. 15 is a perspective view of a tripod type constant a velocityjoint, showing the prior art;

FIG. 16 is a longitudinal sectional view of the tripod type constantvelocity joint of FIG. 15;

FIG. 17 a is a partial sectional view showing the positional relationbetween the roller and the trunnion journal in the prior art tripod typeconstant velocity joint, and FIG. 17 b is a cross-sectional view of thetrunnion journal in FIG. 17 a;

FIG. 18 is a sectional view for explaining a spin moment generated inthe prior art tripod type constant velocity joint;

FIG. 19 is a partial sectional view of another prior art tripod I typeconstant velocity joint; and

FIG. 20 is a three-dimensional view of the trunnion journal.

BEST MODE FOR EMBODYING THE INVENTION

An embodiment of the invention will now be described with reference tothe drawings.

First, referring to FIGS. 1 a, 1 b and 2, a tripod type constantvelocity joint 11 is no different from the one shown in FIGS. 15 and 16described previously, as far as the basic arrangement is concerned,comprising a hollow cylindrical housing 14 fixed to the end of a firstrotary shaft 12, such as a driving shaft, and a tripod 16 fixed to theend of a second rotary shaft 13, such as the rotary shaft on the wheelside.

The housing 14, herein, is formed integrally with the first rotary shaft12, and has axially extending recessed grooves 14 a at circumferentiallytrisectional positions on the inner peripheral surface. Each recessedgroove 14 a is recessed to extend radially outward from the innerperipheral surface of the housing 14, and is composed of a pair ofcircumferentially opposed guide surfaces 14 b and a bottom surfacepositioned on the radially outside of the housing and connecting the twoguide surfaces 14 b. The pair of guide surfaces 14 b provide a racewayfor guiding an outer roller 26, to be later described, axially of thehousing for rolling therein, and torque is transmitted between them andthe outer roller 26. Further, part of the bottom surface of the recessedgroove 14 a is formed with guide shoulder surfaces 14 c for guiding therolling of the outer roller 26. These guide shoulder surface 14 cperform the role of maintaining the posture of the outer roller 26parallel with the housing axis when the outer roller moves in therecessed groove 14 a, ensuring smooth rolling.

The tripod 16 comprises a boss 16 a and a trunnion journal 16 b. Theboss 16 a is fixed to the end of the second rotary shaft 13. Forexample, a spline shaft formed in the second rotary shaft 13 and splineholes formed in the boss 16 a fit together and are positioned by a stopring. The trunnion journals 16 b project radially from circumferentiallytrisectional positions on the boss 16 a. The end of each trunnionjournal 16 b is spherical.

Each trunnion journal 16 b supports a roller assembly 20. The rollerassembly 20 is of a double roller type consisting of an inner roller 22and an outer roller 26 that are relatively turnable through needlerollers 24. The inner peripheral surface of the inner roller 22 is apartial spherical inner peripheral surface having substantially the sameradius of curvature as that of the spherical outer peripheral surface ofthe trunnion journal 16 b. The spherical inner peripheral surface of theinner roller 22 is oscillably supported around the periphery of thespherical outer peripheral surface of the trunnion journal 16 b.

Needle rollers 24 are interposed between the cylindrical outerperipheral surface of the inner roller 22 and the cylindrical innerperipheral surface of the outer roller 26. Therefore, the inner andouter rollers 22 and 26 are capable of relative rotation and axialmovement. In order to prevent slipping-off of the needle rollers 24,needle roller retainers are installed throughout the circumference onboth edge ends of the cylindrical inner peripheral surface of the outerroller 26. As an example of a needle roller retainer, there is shown acase in FIG. 1 a, using retainers 26 a and 26 b separate from the outerroller 26, and a stop ring 25, and FIG. 2 shows another case where aretainer is integral with the outer roller 26. As shown in FIG. 1 b,which is a partial enlarged view of FIG. 1 a, annular retainers 26 a, 26b are installed on both end sides of the needle rollers 24, and stoprings 25 are mounted in stop ring grooves formed in the inner peripheralsurface of the outer roller 26 at both ends.

The outer rollers 26 are received in the recessed grooves 14 a in thehousing 14. A pair of guide surfaces 14 b defining each recessed groove14 a each form substantially the same arc, in the cross-section of thehousing 14, as the generating line of the outer peripheral surface ofthe outer roller 26. Therefore, the outer roller 26 is rollablysupported between these two guide surfaces 14 b.

During the use of the constant velocity joint constructed in the mannerdescribed above, for example, when the first rotary shaft 12 is rotated,the rotary force thereof is transmitted from the housing 14 to the boss16 a of the tripod 16 through the roller assemblies 20 (22, 24, 26) andthe trunnion journals 16 b to rotate the second rotary shaft 13.Further, in the case where the center axes of the first and secondrotary shafts 12 and 13 are out of alignment with each other, in otherwords, they take an operating angle therebetween, with the rotation ofthe two rotary shafts each trunnion journal 16 b is displaced in adirection to swing around the axis of the tripod 16 with respect to theguide surfaces 14 b of the corresponding recessed groove 14 a. At thistime, the outer roller 26 of the roller assembly supported by eachtrunnion journal 16 b rolls on the guide surfaces 14 b of the recessedgroove 14 a while being displaced axially of the trunnion journal 16 b.These movements, as is known in the art, secure equality of velocitybetween the first and second rotary shafts.

As shown at 16 c in FIG. 3, the outer diameter of the boss 16 a isheavily chamfered at one end surface (the left-hand side end surface inFIG. 3) of the boss 16 a of the tripod 16. Thereby, the roller assembly20 can be greatly tilted when it is to be assembled to the trunnionjournal 16 b, and since interference is limited to only two opposedplaces where the trunnion journal 16 b is subjected to a load, pushingin the inner roller 20 attended by elastic deformation makes assemblagepossible. Flat surfaces may be provided for relief at two positions(outside the loading range) at right angles with the position where thetrunnion journal 16 b is subjected to a load.

With the above construction, since torque is transmitted betweenspherical inner peripheral surface of the inner roller 22 and thespherical outer peripheral surface of the trunnion journal 16 b, thecontact surface pressure is kept low, which is advantageous from thestandpoint of strength and durability, making it possible to keep themajor diameter of the contact ellipse relatively small withoutincreasing rotation-directional play, and to decrease the spin moment onthe contact ellipse generated with the swing of the trunnion journal.Therefore, it is possible to avoid more contact than is necessarybetween the recessed groove 14 a in the housing 14 and the one guidesurface 14 c, and the rolling direction of the roller assembly 20 isstabilized, so that it becomes possible to provide a joint wherein therolling resistance in the roller assembly 20 is low and so is the axialforce. As described above, it becomes possible to provide a tripod typeconstant velocity joint ensuring the coexistence of low rollingresistance in the roller assembly and high strength and high durability.

Next, FIGS. 4 a-4 c show modifications in which flat surfaces or dents16 d are provided at or around the center position where the trunnionjournal 16 b is subjected to a load. Flat surfaces or dents of optionalsize are provided in a range where the contact area reduces to ⅕ of thecontact area by spherical fitting without flat surfaces or dents. Thenumber of small flat surfaces or dents is not particularly limited. FIG.4 a shows the case of using a single on the trunnion journal 16 b ¹,FIG. 4 b shows the case of using four on the trunnion journal 16 b ²,and FIG. 4 c shows the case of using a large number on the trunnionjournal 16 b ³. In the case of providing a plurality, a suitablerepetitive pattern or random dispersion may be employed. In the case ofthe embodiment shown in FIGS. 1 a and 2, although the contact stress inthe spherical fitting section is small, the amount of relative slip inthe center of the contact ellipse is at a minimum, so that in the caseof continuous rotation under a load for a long time, poor lubricationtakes place, sometimes leading to a lowering in rotation durability. Themodifications shown in FIGS. 4 a-4 c eliminate such drawbacks.

In a modification shown in FIG. 5 a, both end edges of the cylindricalinner peripheral surface of the outer roller 26 are formed withprojections throughout the periphery to provide integrally formed needleroller retainers 26 a and 26 b. This produces the effect of reducing thenumber of parts. That is, as shown, integrally forming the inner needleroller retainer 26 a and the outer needle roller retainer 26 b on theouter roller 26 makes it possible to constitute the roller assembly byonly three bodies, the inner roller 22, needle rollers 24 and outerroller 26. It is also possible, however, to make either the inner needleroller retainer 26 a or the outer needle roller retainer 26 b integralwith the outer roller 26 while using a separate stop ring or the likefor the other.

A modification shown in FIG. 5 b establishes the relation Di<do where Diis the inner diameter of the inner needle roller retainer 26 a on thecylindrical inner peripheral surface of the outer roller 26, i.e., atthe joint inner diameter side end, the inner diameter of and do is theouter diameter of the inner roller 22. The relation Di<do ensures that,in the state of the tripod kit, i.e., in the unit state of the tripod 16and the roller assemblies 20, the outer roller 26 is hardly disassembledfrom the inner roller 22, and as can be understood from FIG. 1 a, evenif the outer roller 26 moves downward, it interferes with the boss 16 aof the tripod 16 to prevent the needle rollers 24 from disassembling;thus, handling is easy.

In a modification shown in FIG. 6 a, both end edges of the cylindricalouter peripheral surface of the inner roller 22 are provided withprojections throughout the circumference to provide integrally formedneedle roller retainers 22 a and 22 b. This produces the effect ofreducing the number of parts. That is, as shown, integrally forming theinner needle roller retainer 22 a and the outer needle roller retainer22 b on the inner roller 22 makes it possible to constitute the rollerassembly by only three bodies, the inner roller 22, needle rollers 24and outer roller 26. In this case also, it is possible to make eitherthe inner needle roller retainer 22 a, or the outer needle rollerretainer 22 b integral with the inner roller 22 while using a separatestop ring or the like for the other.

A modification shown in FIG. 6 b establishes the relation Di<do where dois the outer diameter of the outer needle roller r retainer 22 b on thecylindrical outer peripheral surface of the inner roller 22, i.e., theouter diameter of the joint outer diameter side end, and Di is the innerdiameter of the outer roller 26. The relation Di<do ensures that, in thestate of the tripod kit, the outer roller 26 is hardly disassembled fromthe inner roller 22, so that handling is easy.

Referring again to FIG. 17 a, in the prior art joint shown in thisfigure, each trunnion journal 8 has two flat portions 8 a perpendicularto the axis z of the tripod 5. The radius r_(T) of the arc generatingthe spherical outer peripheral surface of the trunnion journal 8 issmaller than the radius of curvature, C/2, of the spherical innerperipheral surface of the inner roller 9 a. And the assembling of theinner roller 9 a to the trunnion journal 8 is effected by rotating thetripod 5 around the axis z of the inner roller 9 a by an angle α atwhich the inlet diameter B of the inner roller 9 a (smaller than theinner diameter C) is larger than or equal to a projection A (a) of thediameter A of the spherical outer peripheral surface of the trunnionjournal 8 onto this diameter. In the case of this conventional joint, asshown at 8 b in FIG. 17 b, since a protuberant forged parting lineprojecting from the outer diameter surface of the trunnion journal 8 canbe positioned in the center of the load surface of the trunnion journal,a removing operation such as grinding is inevitable. In order to providea tripod type constant velocity joint ensuring the coexistence ofreduced shudder with the joint assembled to an automobile, highdurability and cost reduction, it is desired that no operation ofremoving the forged parting line of the trunnion journal be required andthat spherical fitting be made possible while holding small theclearance between the spherically surface-fitting inner roller andtrunnion Journal.

Referring to FIGS. 7 a-7 c, the outer peripheral surface of the trunnionjournal 16 b ⁴ is spherical for spherical fitting to the spherical innerperipheral surface of the inner roller 22, but a relief 16 e ispartially formed along the forged parting line 16 p so that theprotuberance of the forged parting line 16 p inwardly recedes from thespherical outer peripheral surface so as not to project outward, asshown in broken line in FIG. 7 c. Therefore, it becomes possible todispense with the step of removing the forged parting line 16 p, and touse the cold molded surface in its molded state, leading to costreduction. In this case, the relief 16 e portion cannot bear a load andhence the loading area is decreased; however, even if the loading rangeis partly decreased, a sufficient load capacity can be held because ofthe type in which the trunnion journal 16 b ⁴ and the inner roller 22cooperate with each other to bear a load by spherical fitting of widerange. FIGS. 7 a-7 c exemplify the case where the relief 16 e is a flatsurface, but a cylindrical surface or some other curved surface may beemployed. Further, in the case of providing the relief 16 e, as comparedwith the case of not providing the relief 16 e, the effect of reducingthe interference margin in assembling the inner roller 22 to thetrunnion journal 16 b ⁴ is obtained, and the amount of elasticdeformation of the inner roller 22 can be made small or eliminated.

Further, in this construction, the inner roller 22 is sphericallysurface-fitted on the trunnion journal 16 b ⁴ and is integrallysupported axially of the trunnion journal 16 b ⁴, so that its movementin the direction of the axis of the trunnion journal accompanyingrotation with an operating angle taken is allowed by rolling slip on theneedle rollers 24 disposed between the inner and outer rollers 22 and26; therefore, the internal friction force is low and a low rollingresistance in rollers is attained. In the case of the prior art shown inFIG. 17 a, when the rollers are to be assembled to the trunnion journal,the rollers are tilted in a plane (corresponding to the plane of FIG. 1a) orthogonal to the plane of FIG. 3. In order to make it possible togreatly tilt the rollers, it is necessary to reduce the outer diameterof the boss, that is, to reduce the thickness of the boss or to prolongthe underhead dimension of the trunnion journal. This, however, causesdrawbacks that if the outer diameter of the boss is reduced, the bossstrength lowers and that if the underhead dimension of the trunnionjournal is increased, the joint outer diameter increases. Thearrangement of FIGS. 7 a-7 c avoids such drawbacks and makes it possibleto provide a tripod type constant velocity joint ensuring thecoexistence of all such factors as low rolling resistance, highstrength, high durability, and cost and size reduction for rollers.

Various concrete forms of the relief 16 e may be contemplated. Thesimplest example is shown in FIG. 8 a wherein part of the spherical isremoved to provide a flat surface 16 e′ on the trunnion journal 16 b ⁵.In the case of providing a relief by simply removing part of thespherical surface, however, the width dimension A of the reliefincreases and the area to bear the load decreases. Thus, for example, asshown in FIG. 9 b, it is possible to form a relief 16 e″ assuming anarcuate shape in the longitudinal section of the trunnion journal 16 b⁶. In this embodiment, there is an advantage that the width dimension Bof the relief is small while the area to bear the load is large.However, both of these embodiments result in a contact state as shown inFIG. 8 b, with a concentrated stress occurring in the edge, causingpremature spalling. Rounding the edge may sometimes fail to besufficiently effective.

What is shown in FIGS. 10 and 20 is an arrangement wherein the outershape of the torque load region of the trunnion journal 16 b ⁷ issubstantially double spherical, having spherical surfaces S1 and S2 asshown in FIG. 20. Concretely, the relation r/2<R<r is established wherer is the radius of curvature of the spherical inner peripheral surfaceof the inner roller 22 and R is the radius of the double sphericalsurface of the trunnion journal 16 b ⁷. In this case, the parting lineposition recedes from the inner spherical surface of the inner rollertoward the minor diameter side, so that a relief 16 e is formed withouttaking special measures. In a torque-loaded state, the contact regionsbetween the trunnion journal 16 b ⁷ and the inner roller 22 are locatedin two positions symmetrical with respect to the forged parting line 16p of the trunnion journal 16 b ⁷.

As shown in FIG. 11, dimensional setting may be such that with θ₁ beingan angle at which the inner roller 22 is about to separate from thetrunnion journal 16 b ⁸ when the inner roller 22 is being tilted withrespect to the trunnion journal 16 b ⁸, at the point of time when theinner roller 22 takes an angle θ₂ that is slightly smaller than θ₁, theouter roller 26 interferes with the second rotary shaft 4 or the stopring 4 a mounted on the second rotary shaft. Employing such arrangementensures that in the state of the unit consisting of the tripod 16 androller assemblies 20, that is, tripod kit, when the tripod 16 isassembled to the second rotary shaft 4 and the stop ring 4 a is mounted,the inner roller 22 interferes with the stop ring 4 a or the secondrotary shaft 4 and cannot tilt up to the angle θ₁ at which it separatesfrom the trunnion journal 16 b ⁸, so that the tripod kit (16, 20) andthe rotary shaft 4 assume a unit handling state, which greatlyfacilitates handling.

In the prior art joint shown in FIG. 17 a, the radius of curvature,r_(T), of the generating line of the trunnion journal 8 is smaller thanthe radius A/2 of the trunnion journal 8 so as to establish the relationø A<ø B when the rollers (9 a, 9 b) are tilted in the circumferentialdirection of the joint with respect to the trunnion journal 8, andspherical fitting is made possible by proving flat surfaces 8 a. In thiscase, however, there are problems that the radius of curvature, r_(T),of the trunnion journal 8 has to be decreased with respect to thecurvature of the inner spherical surface of the inner roller 9 a thatspherically fits on the trunnion journal 8 and that the surface pressureincreases. The assemblage is made possible by setting the sphericalfitting clearance, at a large value instead of by reducing the radius ofcurvature, r_(T), of the trunnion journal 8. In this case, however,there is a problem that the rotation-directional play of the jointincreases. Further, since it is necessary to avoid interference betweenthe root of the trunnion journal disposed circumferentially of the jointsubjected to a torque load and the roller, the enlargement of theunderhead diameter of the trunnion journal is limited. Furthermore, inapplying limit design for size and weight reduction, the root of thetrunnion journal disposed circumferentially of the joint subjected to atorque load probably becomes the lowest strength portion of the trunnionjournal, so that high strength is difficult to secure. Accordingly, in atripod type constant velocity joint of high durability type in whichsurface pressure is reduced by spherical fitting while keeping small theclearance between spherically surface-fitting inner roller and trunnionjournal to keep the rotation-directional play small, it is desired toachieve light-weight compaction and cost reduction while securing thetrunnion journal underhead strength.

Referring to FIGS. 12 a and 12 b, the root of the trunnion journal 16 bis of non-circular cross-section in which the diameter measuredcircumferentially of the joint is larger than the diameter measuredaxially of the joint. FIG. 12 b shows an elliptic shape with its minoraxis directed axially of the joint as a typical example of anon-circular shape in which the diameter measured circumferentially ofthe joint is larger than the diameter measured axially of the joint.

FIG. 13 shows how to assemble the roller assembly 20 to the trunnionjournal 16 b. As shown at 16 c in this figure, only the side of boss 16a of the tripod 16 associated with the end of the second rotary shaft 13(left-hand side end in FIG. 3, right-hand side end in FIG. 2) is heavilychamfered, and the heavy chamfer functions as an interference-avoidingrelief between the trunnion journal 16 b and the roller assembly 20,making it possible to greatly tilt the roller assembly 20 as shown inphantom line in FIG. 3 when the roller assembly 20 is assembled to thetrunnion journal 16 b. And since it is at only two opposed places asseen in the torque load acting direction (the direction perpendicular tothe plane of the sheet of FIG. 3) that the inner roller 22 of the rollerassembly 20 interferes with the trunnion journal 16 b, assemblage ismade possible by pushing in the inner roller 22 while elasticallydeforming the same.

In addition, it is essential only that an interference-avoiding reliefbetween the trunnion journal 16 b and the roller assembly 20 be presentin region of the underhead portion of the trunnion journal disposedaxially of the joint; such relief is unnecessary for the region of thetrunnion journal underhead portion disposed circumferentially of thejoint. With this design specification, since an interference-avoidingrelief in the underhead circumferential position tending to be themaximum stress position when subjected to toque load is unnecessary,strength improvement becomes possible and it is possible to provide amore compact tripod type constant velocity joint. Further, flat surfacesmaybe provided for relief at two places (outside the load range) atright angles with the position subjected to a torque load on thetrunnion journal 16 b.

According to the above construction, it is possible to provide a tripodtype constant velocity joint of high performance type, wherein sincetorque is transmitted between the spherical inner peripheral surface ofthe inner roller 22 and the spherical trunnion journal 16 b, the contactsurface pressure is kept low, a fact which is advantageous for strengthand durability, while the underhead strength of the trunnion journal 16b is also improved, and high performance, high strength, highdurability, and compaction are all satisfied.

As shown in FIGS. 13, 14 a, and 14 b, let θ be the angle at which theinner roller 22 is tilted when assembled to the trunnion journal 16 b.Then, the maximum diameter øD of the trunnion journal 16 b ⁸ includingthe protuberance maximum outer diameter portion of the forged partingline 16 d as projected in the direction of angle B may be set smallerthan the fitting insertion side inner diameter ø d of the inner roller22. Further, as shown in FIGS. 14 a and 14 b, a notch is locally formedin the insertion side inner diameter of the inner roller 22. Let ø d₂the inner diameter of the notch, and ø D₂ be the maximum diameter of thetrunnion journal 16 b ⁸ (including the forged parting line 16 d)projected in the direction of angle θ. Then, these factors may be setsuch that ø D₂<ø d₂. Thereby, when the roller assembly 20 is to beassembled to the trunnion journal 16 b ⁸, it is possible to do sowithout elastically deforming the inner roller 20. Therefore, it becomespossible to dispense with the forged parting line removing step and thepressure-fitting step when the roller assembly 20 is assembled to thetrunnion journal 16 b ⁸.

1. A tripod type constant velocity joint comprising: a hollowcylindrical housing fixed to the end of a first rotary shaft and formedwith axially extending recessed grooves opened at one axial end andlocated at circumferentially trisectional positions on the innerperipheral surface, a tripod consisting of a boss fixed to the end of asecond rotary shaft, and end-spherical trunnion journals radiallyprojecting from circumferentially trisectional positions on the boss,roller assemblies each consisting of an inner roller swingably fitted atthe inner peripheral surface thereof on the spherical outer peripheralsurface of the trunnion journal, and an outer roller supported forrotation and axial movement on the outer peripheral surface of the innerroller through needle rollers, wherein the outer rollers are received inthe recessed grooves in the housing and are rollable axially of thehousing, each recessed groove consists of guide surfaces contacting theouter peripheral surface of the outer roller and subjected to loads, andguide shoulder surfaces for guiding the outer roller axially of thehousing, and only side of the outer diameter of said boss associatedwith the end of the second rotary shaft is heavily chamfered.
 2. Atripod type constant velocity joint as set forth in claim 1, whereinflat surfaces or dents are formed at load-imposed positions on thespherical outer peripheral surface of the trunnion journal.
 3. A tripodtype constant velocity joint as set forth in claim 1, wherein at leastone end of the inner peripheral surface of the outer roller isintegrally provided with a needle roller retainer.
 4. A tripod typeconstant velocity joint as set forth in claim 1, wherein at least oneend of the outer peripheral surface of the inner roller is integrallyprovided with a needle roller retainer.
 5. A tripod type constantvelocity joint as set forth in claim 1, wherein the inner diameter ofthe cylindrical inner peripheral surface of the outer roller at thejoint inner diameter side end is smaller than the outer diameter of theinner roller.
 6. A tripod type constant velocity joint as set forth inclaim 1, wherein the outer diameter of the cylindrical outer peripheralsurface of the inner roller at the joint outer diameter side end issmaller than the inner diameter of the outer roller.